The Letter Carrier's Rounds |
For an electronic mail application you are to describe the SMTP-based communication that takes place between pairs of MTAs. The sender's User Agent gives a formatted message to the sending Message Transfer Agent (MTA). The sending MTA communicates with the receiving MTA using the Simple Mail Transfer Protocol (SMTP). The receiving MTA delivers mail to the receiver's User Agent. After a communication link is initialized, the sending MTA transmits command lines, one at a time, to the receiving MTA, which returns a three-digit coded response after each command is processed. The sender commands are shown below in the order sent for each message. There is more than one RCPT TO line when the same message is sent to several users at the same MTA. A message to users at different MTAs requires separate SMTP sessions.
HELO myname Identifies the sender to the receiver (yes, there is only one L)
MAIL FROM:< sender > Identifies the message sender
RCPT TO:< user > Identifies one recipient of the message
DATA Followed by an arbitrary number of lines of text comprising the message
body, ending with a line containing a period in column one.
QUIT Terminates the communication.
The following response codes are sent by the receiving MTA:
MTA London 4 Fiona Paul Heather Nevil MTA SanFrancisco 3 Mario Luigi Shariff MTA Paris 3 Jacque Suzanne Maurice MTA HongKong 3 Chen Jeng Hee MTA MexicoCity 4 Conrado Estella Eva Raul MTA Cairo 3 Hamdy Tarik Misa * Hamdy@Cairo Conrado@MexicoCity Shariff@SanFrancisco Lisa@MexicoCity * Congratulations on your efforts !! --Hamdy * Fiona@London Chen@HongKong Natasha@Paris * Thanks for the report! --Fiona * *
Connection between Cairo and MexicoCity HELO Cairo 250 MAIL FROM:<Hamdy@Cairo> 250 RCPT TO:<Conrado@MexicoCity> 250 RCPT TO:<Lisa@MexicoCity> 550 DATA 354 Congratulations on your efforts !! --Hamdy . 250 QUIT 221 Connection between Cairo and SanFrancisco HELO Cairo 250 MAIL FROM:<Hamdy@Cairo> 250 RCPT TO:<Shariff@SanFrancisco> 250 DATA 354 Congratulations on your efforts !! --Hamdy . 250 QUIT 221 Connection between London and HongKong HELO London 250 MAIL FROM:<Fiona@London> 250 RCPT TO:<Chen@HongKong> 250 DATA 354 Thanks for the report! --Fiona . 250 QUIT 221 Connection between London and Paris HELO London 250 MAIL FROM:<Fiona@London> 250 RCPT TO:<Natasha@Paris> 550 QUIT 221